System for controlling the flow of a fluid through a substrate

ABSTRACT

A system is described for controlling the flow of a sample fluid through a substrate having first and second surfaces and at least one area with a plurality of through-going capillary channels. The system comprises a housing having a chamber for receiving the substrate and a pressure differential generator capable of generating and maintaining a pressure difference over the substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional PatentApplication Serial No. 60/297,592, filed Jun. 11, 2001, and EuropeanPatent Application 01200946.0, filed Mar. 13, 2001.

BACKGROUND OF THE INVENTION

[0002] (1) Field of the Invention

[0003] The present invention relates to a system for controlling theflow of a fluid, in particular a sample fluid, through a substratehaving first and second surfaces and at least one area with a pluralityof through-going capillary channels.

[0004] (2) Description of the Related Art

[0005] A system of this type is described in PCT/US00/24885. In thissystem means are provided for applying and/or maintaining a sufficientamount of time a controlled pressure difference. The pressure differencecan be regulated by a programmable unit.

SUMMARY OF THE INVENTION

[0006] The invention aims to provide an improved system of this type.According to the invention the system comprises a housing having achamber for receiving the substrate and a pressure differentialgenerator capable of generating and maintaining a pressure differenceover the substrate. The invention will be further explained by referenceto the drawings showing an embodiment of the system of the invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0007]FIG. 1 schematically shows an embodiment of the system of theinvention.

[0008]FIG. 2 shows a cross-section of the housing of the system of FIG.1, wherein a substrate is accommodated in the housing.

[0009]FIG. 3 shows a perspective view of an example of the substrateshown in cross-section in FIG. 2.

[0010]FIG. 4 shows a cross-section of the housing of FIG. 2, wherein awashing device is placed on the housing.

DETAILED DESCRIPTION OF THE INVENTION

[0011] Referring to FIG. 1, there is shown a system for controlling theflow of a sample fluid through a substrate 1 which is shown in aperspective view by way of example in FIG. 3. In this embodiment thesubstrate 1 is made as a laminated array-membrane comprising upper andlower outer layers 2 and an intermediate strip of aluminium oxide. Theouter layers 2 are provided with four openings 3, the openings 3 of theupper and lower layers 2 being aligned. In this manner the strip ofaluminium oxide is exposed at four areas or wells 4. The strip ofaluminium oxide comprises a large number of through-going capillarychannels oriented mainly perpendicular to the upper and lower surfacesof the strip. The capillary pressure of the channels is very high. In apractical embodiment of the substrate 1, the channels in the strip ofaluminium oxide may have a spacing of approximately 150-200 nm, whereina binding substance is bound to the substrate in groups of channels at aspacing of 200 mm. A group of channels can be indicated as a dot or dotarea. Each area 4 of the substrate 1 may have approximately 400 dots.For a further description of the substrate reference is made to theabove-mentioned international patent application PCT/US00/24885. It willbe understood that the number of exposed areas of the substrate, thenumber of dots and the dimensions are mentioned by way of example onlyand may be varied as desired.

[0012] The system shown in FIGS. 1 and 2 comprises a housing 5 having anupper housing part 6 and a lower housing part 7. The upper and lowerhousing parts 6, 7 determine a chamber 8 for receiving the substrate 1.As shown in FIG. 2, the substrate 1 is received in the chamber 8together with a holding device 9 which includes an upper and lowerstructure 10 and 11, respectively. Both upper and lower structures 10,11 are provided with four cylindrical extensions 12 mainly aligned withthe areas 4 of the substrate 1. The holding device 9 is made of aplastic material. The device 9 is further described in a co-pendingpatent application “Device for holding a substrate” of the sameapplicant, European Patent Application 01200947.8, filed Mar. 13, 2001.

[0013] The chamber 8 comprises cylindrical chamber sections 13 in theupper and lower housing parts 6, 7, in which the cylindrical extensions12 are received. In the upper housing part 6, these cylindrical chambersections 13 are interconnected by a channel 14 providing a connectionbetween the cylindrical chamber sections 13 and the environment of thehousing 5, so that an ambient pressure reference is available in theseupper cylindrical chamber sections 13.

[0014] In the lower housing part 7, the cylindrical chamber sections 13are also interconnected by a channel 15. In this case the channel 15 isconnected to a means for generating a pressure difference over thesubstrate 1. In the embodiment shown the means for generating a pressuredifference over the substrate 1 is made as means to change the volume ofthe chamber 8, in this case the part of the chamber 8 under thesubstrate 1. More particularly, the means for generating a pressuredifference are implemented as a cylinder piston assembly 16schematically shown in FIG. 1.

[0015] In FIG. 2, a sample fluid 17 is schematically shown in twocylindrical extensions 12 of the device 9, so that only at thecorresponding areas 4 of the substrate 1 the sample fluid can be passedthrough the capillary channels of the substrate 1. As schematicallyindicated by means of sealing rings 18, two cylindrical chamber sections13 are sealed with respect to the channel 15 so that a pressuredifference over the substrate 1 is only generated at the areas 4 where asample fluid 17 is present.

[0016] During transporting the sample fluid 17 through the capillarychannels of the substrate 1, substances in the sample fluid can be boundby the binding substance in these capillary channels. In order to allowa mutual comparison of test results, it is important to accuratelycontrol the time period for transporting the sample fluid through thesecapillary channels. In order to control this transport time in anaccurate manner, the system shown in FIG. 1 is provided with means 19for maintaining the pressure difference over the substrate at acontrolled level during the transport of the sample fluid 17 through thecapillary channels. Generally, said means 19 will be implemented in aprogrammable processing unit. Preferably the pressure difference ismaintained at a constant level during the transport of the sample fluid.In order to determine the time period during which the sample fluid 17is transported through the capillary channels of the substrate 1, theprocessing unit 19 comprises means for setting a desired pressuredifference.

[0017] As mentioned, the means for generating a pressure difference overthe substrate to transport the sample fluid 17 from the upper surface ofthe substrate 1 to the lower surface is implemented as a cylinder pistonassembly 16 having a piston 20 which is moveable by means of aschematically indicated actuator 21. This actuator 21 or control deviceis controlled by the processing unit 19 in dependence on the pressure inthe chamber 8 as measured by means of a schematically indicated pressuremeasuring device 22. Assuming that at the beginning of an assay thesample fluid 17 is located in the upper cylindrical extensions 12, theprocessing unit 19 starts to generate a pressure difference over thesubstrate 1 by generating in the chamber 8 under the substrate 1 apressure lower than the ambient pressure. This pressure differencetransports the sample fluid 17 through the capillary channels of thesubstrate 1 so that the sample fluid 17 will gradually be transportedtowards the lower cylindrical extensions 12 of the lower structure 11.This would result in an increase of the pressure in the chamber 8 underthe substrate 1 and this pressure increase is measured by the measuringdevice 22. In view of this pressure increase as measured by theprocessing unit 19, the processing unit 19 operates the actuator 21 todisplace the piston 20 to maintain the pressure difference at a constantlevel. In this manner the sample fluid 17 is transported through thecapillary channels of the substrate 1 in an accurately determined timeperiod.

[0018] Generally the sample fluid 17 should be transported through thecapillary channels of the substrate 1 a number of times in order toallow for a sufficient binding action of the binding substance in thecapillary channels of the substrate 1. In order to reduce the overalltime of the assay, it is important to reduce the time required forreversing the transport of the sample fluid through the capillarychannels. In the system described, the time for reversing the transportis reduced by monitoring the operation of the processing unit 19 formaintaining the pressure difference at a constant level. As soon as theprocessing unit stops to operate the actuator 21 for maintaining thepressure difference at a constant level, the pressure difference overthe substrate is changed immediately in such a manner that the samplefluid 17 is transported in the reverse direction from the lower surfaceof the substrate 1 towards the upper surface through the capillarychannels. For, as soon as the pressure difference remains constantwithout any displacement of the piston 20, this is an indication thatthe sample fluid 17 is completely transported through the capillarychannels of the substrate 1. To change the pressure difference, thepiston 20 is displaced in the opposite direction by the actuator 21.Thereby, the sample fluid 17 is transported towards the upper surface ofthe substrate 1. Thereby the pressure in the chamber 8 under thesubstrate 1 would decrease and this is measured by the measuring device22. The processing unit 19 operates the actuator 21 to displace thepiston 20 to maintain the pressure difference at a constant level. Inthis manner the sample fluid 17 can be transported in oppositedirections through the capillary channels of the substrate 1 in aminimum time period.

[0019] It is noted that the pressure difference required to transportthe sample fluid 17 through the capillary channels of the substrate 1 ismuch lower than the capillary pressure of the capillary channels of thesubstrate 1. In this manner it is prevented that the sample fluid 17 ispushed off the upper or lower surface of the substrate 1 when the samplefluid is completely transported through the channels.

[0020] In the system described, the processing unit 19 is adapted tomeasure the change of volume required to transport the sample fluid 17completely through the capillary channels from the upper to the lowersurface and vice versa. The change of volume can be measured for exampleby measuring the displacement of the piston 20. This change of volumeshould be constant for each transport step of the system, i.e. each timethe sample fluid 17 is transported from the upper to the lower surfaceor vice versa. If the change of volume required to completely transportthe sample fluid varies, this is an indication that a leak is presentsomewhere in the system so that the system should be checked by anoperator. The processing unit 19 can provide a warning indication tosignal an operator a variation in the change of volume.

[0021] Further, the processing unit 19 can measure the change of volumerequired to transport the sample fluid completely through the capillarychannels of the substrate 1 in order to compare this change of volumewith the initial volume of the sample fluid 17 provided in thecylindrical extensions 12. This initial volume can be provided as aninput to the processing unit 19. As an alternative, the processing unit19 could also be used to automatically provide a predetermined initialvolume in the cylindrical extensions 12 for performing an assay. If adifference between the initial volume and the required change of volumeis measured, this is also an indication of a leak in the system. Thisdifference can be indicated by the processing unit 19 to warn anoperator.

[0022] A further advantage of the system described is that theprocessing unit 19 can measure the time to transport the sample fluidthrough the capillary channels of the substrate 1, i.e. the flow rate.If this time or flow rate varies this is an indication that an airbubble or a contamination is blocking at least a part of the capillarychannels. As the flow resistance of the substrate and the pressure usedto transport the fluid are known or can be established, the processingunit 19 can determine the flow rate and/or the time required totransport an amount of the sample fluid through the substrate. Anydeviation from the expected time or flow rate can be used as anindication of an error situation.

[0023] The system described shows the advantage that a washing operationto clean the capillary channels of the substrate 1 can be carried out inan easy manner. According to FIG. 4 a washing device 23 is placed on topof the housing 5 after removal of an upper glass cover 24 normallylocated on top of the housing S. The glass cover allows a direct visionon to the upper surface of substrate areas 4 during transport of thesample fluid 7 through the channels. The washing device 23 is providedwith washing fluid feed and discharge tubes 25 and 26. Washing isperformed in a programmable manner. For example, a all washing fluid canbe can be fed on top of the substrate 1, the washing fluid can betransported through the capillary channels of the substrate 1 a numberof times and the washing fluid can be discharged. Discharging of thewashing fluid may occur for example in a continuous flow at a slightlyhigher rate than feeding. If the processing unit 19 generates a positivepressure under the substrate 1 the washing fluid will stay on top of thesubstrate 1. By generating a negative pressure under the substrate 1,the washing fluid is transported through the capillary channels of thesubstrate 1 to the lower side in the same manner as described for asample fluid. By reversing the pressure difference the washing fluid istransported back to the upper side of the substrate 1 again. In thismanner the capillary channels of the substrate can be cleaned in anefficient manner. Contamination of the channel 15 is prevented as thewashing fluid will not be pushed off of the lower side of the substrate1. The washing device is connected to a source of washing fluid notshown by means of schematically indicated tubes 27. The washingoperation is controlled by the processing unit 19.

[0024] Other embodiments within the scope of the claims herein will beapparent to one skilled in the art from consideration of thespecification or practice of the invention as disclosed herein. It isintended that the specification be considered exemplary only, with thescope and spirit of the invention being indicated by the followingclaims.

[0025] In view of the above, it will be seen that the several advantagesof the invention are achieved and other advantages attained.

[0026] As various changes could be made in the above methods andcompositions without departing from the scope of the invention, it isintended that all matter contained in the above description and shown inthe accompanying drawings shall be interpreted as illustrative and notin a limiting sense.

[0027] All references cited in this specification are herebyincorporated by reference. The discussion of the references herein isintended merely to summarize the assertions made by the authors and noadmission is made that any reference constitutes prior art. Applicantsreserve the right to challenge the accuracy and pertinence of the citedreferences.

What is claimed is:
 1. A system for controlling the flow of a fluidthrough a substrate having first and second surface and at least onearea with a plurality of through-going capillary channels, characterizedby a housing having a chamber for receiving the substrate, means forgenerating a pressure difference over the substrate to transport thesample fluid from the first to the second surface or vice versa throughthe channels of said at least one area, and means for maintaining thepressure difference at a controlled level during the transport of thefluid through the channels.
 2. The system of claim 1, wherein the fluidis a sample fluid.
 3. The system of claim 1, wherein the maintainingmeans comprises means for setting a desired level of the pressuredifference.
 4. The system of claim 1, wherein the means for generating apressure difference comprise means to change the volume of the chamber,wherein the maintaining means comprises a pressure measuring device anda control device to operate the volume changing means.
 5. The system ofclaim 3, wherein the means for generating a pressure difference comprisemeans to change the volume of the chamber, wherein the maintaining meanscomprises a pressure measuring device and a control device to operatethe volume changing means.
 6. The system if claim 1, comprising meansfor monitoring the operation of the maintaining means, wherein saidmonitoring means are adapted to change the pressure difference over thesubstrate to transport the fluid in the reverse direction through thechannels as soon as the operation of the maintaining means shows thatthe fluid has been transported through the substrate.
 7. The system ifclaim 3, comprising means for monitoring the operation of themaintaining means, wherein said monitoring means are adapted to changethe pressure difference over the substrate to transport the fluid in thereverse direction through the channels as soon as the operation of themaintaining means shows that the fluid has been transported through thesubstrate.
 8. The system of claim 4, wherein the monitoring meansmonitor the operation of said maintaining means, wherein the pressuredifference is changed to transport the fluid in reverse direction assoon as the pressure difference remains at a constant level withoutoperation of the maintaining means.
 9. The system of claim 6, whereinthe monitoring means monitor the operation of said maintaining means,wherein the pressure difference is changed to transport the fluid inreverse direction as soon as the pressure difference remains at aconstant level without operation of the maintaining means.
 10. Thesystem of claim 4, wherein the volume changing means comprises acylinder piston assembly connected to the chamber and wherein saiddevice operates the piston of the cylinder piston assembly.
 11. Thesystem of claim 6, wherein the volume changing means comprises acylinder piston assembly connected to the chamber and wherein saiddevice operates the piston of the cylinder piston assembly.
 12. Thesystem of claim 4, wherein the pressure difference is changed in thereverse direction by reversing the change of volume.
 13. The system ofclaim 6, wherein the pressure difference is changed in the reversedirection by reversing the change of volume.
 14. The system of claim 4,further comprising means for measuring the change of volume required totransport the fluid through the channels from the first to the secondsurface or vice versa, wherein said measuring means is adapted toindicate if said change of volume is varying in successive transports ofthe fluid through the channels.
 15. The system of claim 6, furthercomprising means for measuring the change of volume required totransport the fluid through the channels from the first to the secondsurface or vice versa, wherein said measuring means is adapted toindicate if said change of volume is varying in successive transports ofthe fluid through the channels.
 16. The system of claim 14, comprisingmeans to input the initial volume of a sample fluid, wherein saidmeasuring means is adapted to compare said initial volume and saidchange of volume, wherein said measuring means provides an indication ifa difference is established.
 17. The system of claim 4, comprising meansfor measuring the time required to transport the fluid through thechannels from the first to the second surface or vice versa, whereinsaid measuring means is adapted to indicate if the measured timeindicates a variation of fluid flow rate.
 18. The system of claim 6,comprising means for measuring the time required to transport the fluidthrough the channels from the first to the second surface or vice versa,wherein said measuring means is adapted to indicate if the measured timeindicates a variation of fluid flow rate.
 19. The system of claim 4,comprising a washing device having washing fluid feed and dischargetubes wherein the washing device is adapted to supply and remove washingfluid to and from the chamber as controlled by the maintaining means.20. The system of claim 6, comprising a washing device having washingfluid feed and discharge tubes wherein the washing device is adapted tosupply and remove washing fluid to and from the chamber as controlled bythe maintaining means.